add type: Timestamp with nanosecond units

[jacobmarble]

Feature Request / Improvement

As discussed in the mailing list, and described in this doc, I'd like to add two new types to Iceberg: timestamp_ns and timestamptz_ns.

These types represent timestamps using nanosecond units since Epoch, rather than microseconds.

The design doc as of 19-sep-2023:
Nanosecond Timestamps in Apache Iceberg 19-sep-2023.pdf

Query engine

None

[jacobmarble]

Maintainers: This issue can be assigned to me.